This invention relates to an apparatus for continuous electrolytic treatment of an aluminum article such as a web, wire or foil made of aluminum or an alloy thereof, particularly to an apparatus for electrolytic treatment capable of solving problems occurred during a high speed driving of an electrolytic line and during electrolysis of a thick film.
A continuous electrolytic treatment has been usually utilized in a wide range such as an anodic oxidation, an electrolytic colouring, an electrolytic polishing and an electrolytic etching, used in manufacturing of a support for a printing plate, an alumite wire, an electrolytic capacitor or the like.
A conventional continuous electrolytic treatment for an aluminum product was conducted by the electrolytic treatment disclosed in Japanese Patent KOKAI Nos. 48-26638 and 47-18739 and Japanese Patent KOKOKU No. 58-24517, and the method is usually referred to as the submerged power supply system. An apparatus for the electrolytic treatment according to the submerged power supply system is shown in FIG. 4. This apparatus is in a type of the anodic oxidation using direct current and is composed of three parts, i.e. a power supply part 2 for charging an aluminum article 1 with a negative charge 7 and electrolytic part 3 for the electrolytical treatment of the aluminum article 1 charged with negative charge and an intermediate part 4 for preventing a short in the liquid between the power supply part 2 and the electrolytic part 3. A power supply electrode 5 and an electrolytic electrode 6 are disposed in the electrolyte solution of the power supply part 2 and the electrolytic part 3, and the power supply electrode 5 is connected to the electrolytic electrode 6 through a direct current source 7.
In the apparatus for electrolytic treatment, the electric current from the direct current source 7 flows to the aluminum product 1 through the electrolyte solution from the power supply electrode 5 in the power supply part 2, flows in the direction of the electrolytic part 3 in the aluminum article 1 and flows to the electrolytic electrode 6 through the electrolyte solution from the aluminum product 1 in the electrolytic part 3. Thus, an oxide film by the anodic oxidation is formed on the surface of the aluminum article 1. In the submerged power supply system, since the article to be treated is not contacted with an electrode or the like, the occurrence of spark during supplying electricity, the occurrence of damages and the like are prevented. Therefore, a line of an electrolytic treatment having a high stability can be provided.
However, there were some problems in the above mentioned apparatus for electrolytic treatment. First, the speedup of a line of electrolytic treatment and the increase in a thickness of the oxide film by the anodic oxidation can not be conducted in low cost. That is, at the case that the line of electrolytic treatment is speeded up for improving productivity and in the case that the thickness of the oxide film by the anodic oxidation is increased for improving quality, an amount of supply current is necessarily increased, a voltage drop caused by ohmic loss is increased in the aluminum article, with increasing a supply current. Therefore, an increase in the electrolytic voltage of a source is necessary.
When the electrolytic voltage is increased, since the electric energy is increased, the running cost is increased, and since a capacity of the source is necessarily large, the plant investment is increased. Besides, since an electrolytic voltage is great, Joule heat greatly generates in the aluminum article between the power supply electrode 5 and the electrolytic electrode 6. As a result, a cooling cost for cooling the aluminum article and the electrolyte solution to a prescribed normal temperature increases. As described above, when the line of electrolytic treatment is speeded up in the conventional apparatus, the cost becomes too great.
Second, in the case that the aluminum article has a small sectional area, the speedup of the line for electrolytic treatment is difficult. That is, since the whole current supplied by a power source flows into the aluminum article at the intermediate part between the power supply part and the electrolytic part, when the amount of supplied current is great, the aluminum article having a small sectional area such as a wire, a foil and a thin web heats up greatly and fuses. Therefore, in the case of the aluminum article having a small sectional area, there is a limit in an amount of supplying current. As a result, the speedup of a line for electrolytic treatment and the increase in a thickness of an oxide film by the anodic oxidation are difficult.
Third, countermeasures for preventing corrosion, leakage and the like are necessary. That is, when a process using an organic solvent such as a coating process is necessary as a post-process of the electrolytic treatment, the aluminum article after the electrolytic treatment process is generally grounded through a means such as a grounding roll in order to prevent explosion, flash and the like caused by the elevation of electric potential of the aluminum article in the post-process. However, in this case, though the electric potential of the aluminum article after the electrolytic treatment bath is kept at almost the same electric potential as the electric potential of the earth, the electric potential of the aluminum product prior to the electrolytic treatment bath is kept at a greater electric potential than the electric potential of the electrolytic treatment bath. Electric current flows accordingly formed in the line through the aluminum article, and then comes back to the direct current source through the pre-treatment apparatus and the post-treatment apparatus for the electrolytic treatment apparatus. As a result, a circuit composed of the aluminum article, the pre-treatment apparatus, the post-treatment apparatus and the like occurs. Troubles, such as corrosion of metal members used in a pipe and a pump, spark trouble and leakage, occur in various treatment apparatuses wherein a pre-treatment of the electrolytic treatment apparatus is conducted by such an electric current.
Therefore, a non-corrosive material or an insulating material must be used in order to prevent the occurrence of the troubles, facilities accordingly become complex. As a result, the facilities cost and the maintenance cost increase greatly. Moreover, when the line for electrolytic treatment is speeded up in order to improve productivity, or when the thickness of the oxide film by the anodic oxidation is increased in order to improve a quality, to elevate an amount of the electric current supply is necessary, electric potential accordingly become greater at the aluminum article before the electrolytic treatment bath than the electric potential of the bath, and this point was particularly great problem.